14.8. NIS — Network Information Service

As soon as multiple UNIX systems in a network want to access common
resources, it becomes important that all user and group identities are the
same for all machines in that network. The network should be transparent to
the user: whatever machine a user uses, he will always find himself in
exactly the same environment. This is made possible by means of NIS and NFS
services. NFS distributes file systems over a network and is discussed in
Section 14.9. “NFS — Shared File Systems”.

NIS (Network Information Service) can be described as a database-like service
that provides access to the contents of /etc/passwd,
/etc/shadow, and /etc/group across
networks. NIS can also be used for other purposes (to make available the
contents of files like /etc/hosts or
/etc/services, for instance), but this is beyond the
scope of this introduction. People often refer to NIS under the term of
“YP”, which simply stands for the idea of the network's
“yellow pages”.

14.8.1. NIS Master and Slave Servers

For the configuration, select ‘NIS Server’ from the YaST
module ‘Network Services’. If no NIS server existed so far
in your network, activate ‘Install and set up a Master NIS
Server’ in the next screen. If you already have a NIS server (a
master), you can add a NIS slave server (for example,
if you want to configure a new subnetwork). First, the configuration of the
master server is described.

If some needed packages are missing, insert the respective CD or DVD as
requested to install the packages automatically. Enter the domain name at
the top of the configuration dialog, which is shown in Figure 14.5. “YaST: NIS Server Configuration Tool”. With the check box below, define whether
the host should also be a NIS client, enabling users to log in and access
data from the NIS server.

To allow users in your network (both local users and those managed through
the NIS server) to change their passwords on the NIS server (with the
command yppasswd), activate the corresponding option.
This makes ‘Allow Changes to GECOS
Field’ and ‘Allow Changes to Login
Shell’ available.
“GECOS” means that the users can also change their names and
address settings with the command ypchfn.
“SHELL” allows users to change their default shell with the
command ypchsh, for example, to switch from
bash to sh.

By clicking ‘Other Global Settings...’, access a screen,
shown in Figure 14.6. “YaST: Changing the Directory and Synchronizing Files for a NIS
Server”, in
which to change the source directory of the NIS server (/etc by default). In addition, passwords and
groups can be merged here. The setting should be
‘Yes’ so the files (/etc/passwd,
/etc/shadow, and
/etc/group) can be synchronized. Also
determine the smallest user and group ID. Press
‘OK’ to confirm your
settings and return to the previous screen. Then click
‘Next’.

Figure 14.6. YaST: Changing the Directory and Synchronizing Files for a NIS
Server

If you previously enabled ‘Active Slave NIS Server Exists’,
enter the host names used as slaves and click ‘Next’. If
you do not use slave servers, the slave configuration is skipped and you
continue directly to the dialog for the database configuration. Here,
specify the maps, the partial databases to transfer
from the NIS server to the client. The default settings are
usually adequate, so normally they should be left unchanged.

The first one enables connections from your own host, which is the NIS
server. The second one allows all hosts with access to the same network to
send requests to the server.

Figure 14.7. YaST: Setting Request Permissions for a NIS Server

14.8.2. The NIS Client Module of YaST

This module facilitates the configuration of the NIS client. After
choosing to use NIS and, depending on the circumstances, the
automounter, this dialog opens. Select whether the host has a fixed
IP address or receives one issued by DHCP. DHCP also provides the NIS domain
and the NIS server. For further information about DHCP, see Section
14.10. “DHCP”. If a static IP address is used,
specify the NIS domain and the NIS server manually (see Figure 14.8. “Setting Domain and Address of NIS Server”). The button
‘Find’ makes YaST search for an active NIS server in your
network.

In addition, you can specify multiple domains with
one default domain. Use ‘Add’ to specify multiple servers
including the broadcast function for the individual domains.

In the expert settings, check ‘Answer to the Local Host
Only’, if you do not want other hosts to be able to query which
server your client is using. By checking ‘Broken Server’,
the client is enabled to receive replies from a server communicating through
an unprivileged port. For further information, see
manypbind.